1. Field of the Invention
The present invention relates to drum brake shoes and brake lining blocks for vehicles such as trucks or buses.
2. Background Art
Vehicle brakes are generally either disk brakes or drum brakes. Drum brakes are generally preferred for buses and commercial trucks because drum brakes may provide a greater surface area of friction material. The braking surface of the friction material is generally riveted to a backing plate of a brake block. Generally, 12 to 16 rivets are required to attach a brake block to a brake shoe due to the substantial shear forces that must be withstood during braking between the brake blocks and the brake shoe.
Commercial and industrial vehicle brake linings that are riveted to steel brake shoes are generally rigid, non-asbestos friction material. If the outer diameter of the brake shoe surface that is to be retrofit with new brake linings is not completely flat or within original design radius tolerances, the lining after fastening to the shoe may crack or break off of the brake shoe. This may create problems relating to braking performance and durability.
The friction material used on brake blocks is drilled and countersunk to receive rivets that are used to connect the brake block to the brake shoe. Holes are formed in the friction material by either a drilling or a punch operation. If the counter bore is not drilled deep enough, the brake block may crack when riveted to the to the brake shoe by a riveter. If the counter bore is drilled too deep, the brake block may be only loosely fastened that can lead to cracking of the friction material or other problems.
If the rivet tool misses a rivet location and contacts the friction material, may harm the friction material. The friction material may be cracked, broken, or deformed if the rivet is misdirected, or improperly set-up for depth and force. Any cracking, breakage or deformation could adversely impact braking performance of the lined brake shoe when installed on a vehicle.
Substantial labor costs are incurred to rivet brake blocks to a brake shoe. Additional expenses may be incurred if it is necessary to scrap a cracked brake block.
The surface area of the friction material is reduced by each access hole in the friction material required for a rivet. Any reduction in surface area of the friction material may adversely affect stopping performance. Holes for rivets in the surface of the friction material may result in unwanted noise especially if dirt or other foreign material is permitted to collect in the rivet access holes.
It has been proposed to integrally mold rivets into the backing plate of the brake block. Another attaching mechanism proposed for brake blocks is the use of clinch nuts, however, clinch nuts are generally only usable with transit bus brakes due to the high profile of the clinch nuts.
In the manufacture of brake blocks, problems may be encountered including blistering at the corners of the brake blocks. The corners of brake blocks may be broken or damaged especially if the corners are formed with right angle corners.
There is a need for an improved brake shoe having brake blocks that maximize the friction material surface area while minimizing riveting operations. There is also a need to eliminate the potential for damage to friction material on brake blocks when they are assembled to a brake shoe. Applicant's invention is directed to solving the above problems as summarized below.